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HMT Wx Forecast made 1945z 9 Feb 08

Outlook for the next several days is dry. The current pattern of ridging in the eastern Pacific and mean upper trough position over the CONUS is expected to hold for the next week at least. It is worth noting that the NCEP global ensemble members, visible on the Penn State Ewall page, are amazingly dry out through 10 days. Only 2 of the 12 indicate any pcpn over the American RIver Basin for the 10-d period ending 1200 UTC 19 Feb, and both of these show < 0.10" total for that entire 10-d period. The ECMWF and GFS hi res runs are more similar than usual, and the EC is also showing ZERO accumulated pcpn over the ARB for the same 10-d period.

Two short-wave troughs will pass over the area in the next few days. The first of these is approaching the Northwest coast at present and giving some light pcpn in western WA and nw OR. I doubt any pcpn will fall anywhere in CA out of this weakening feature, which is now within mid-level larger scale difluence. A second, stronger storm now in the central Pacific will approach the coast Tu 12 Feb. The ECMWF and GFS are indicating the usual weakening of the surface low as it approaches the coast. The upper level portion of this feature will split as it enters the mean difluence near the coast, with the southern portion heading southeastward to form a cutoff low over srn CA/AZ/Sonora. As this feature passes over the area late Tu 12 Feb on its way southeastward, there exists the possibility of a few inches of orographic snow over the higher ridges of the Sierra. However, mosture will be limited and the flow not favorable for terrain forced lift (700mb flow may not get out of the NW quadrant), so I would be surprised to see amounts greater than 1/4" to 1/3" at best, and this only if this feature digs farther W than forecast.

Beyond this, the outlook is poor for the last half of next week. By the weekend, the global models are indicating that the present strong jet coming off the Asian coast and across the western Pacific will extend farther east. (At present, and for the last several days the strong jet has terminated in an upper difluent region between HI and AK, with mean low-latitude troughing SE of HI and higher latitude ridging over the eastern Pacific.) This may eventually pave the way for a shifting inland of the ridge now over the eastern Pacific and for a greater potential for IOPs the week of Presidents' Day.

John B.